Document handler vacuum belt platen transport clamping system

ABSTRACT

A document handler 20 for presenting documents to the platen 23 of a copier 10 for copying with a vacuum belt platen transport system 32 having document transporting belts 35 movable under a substantially planar vacuum plenum backing and imaging background surface 33a overlying the platen, and a vacuum system 33 for applying a partial vacuum to a document sheet being transported by the movable belts over the platen; with a clamping and unclamping system for moving the vacuum plenum backing and imaging background surface 33a against the platen 23 to flatten the belts 35 and a document thereon against the platen for copying. During unclamping the surface 33a slightly fits away from the platen, while supplying the partial vacuum to lift a document away from the platen retained on the belts, by first lifting a first side of the surface 33a up away from the platen substantially before the opposite side, and then subsequently lifting the opposite side, to generate a controlled air flow for assisting in retaining the documents to the belts, and moving the belts when the surface is lifted away from the platen. During clamping the first side of the surface 33a moves towards the platen beginning slightly before the opposite side to generate a controlled air flow expulsion of air.

Hereby cross-referenced, and incorporated by reference, is the copendingapplication of the same assignee, U.S. Serial No. 029,027, now U.S. Pat.No. 4,794,42, entitled "Automatic Dual Mode Sheet and Web DocumentTransport For Copiers" Filed Mar. 23, 1987 by the same Thomas Acquaviva(sole) (Attorney Docket No.D/86036).

The present invention relates to copier document handling, and, moreparticularly, to the improved transporting and positioning of documentsfor copying over the platen of a copier with a vacuum belt documenttransport system for an automatic document handling system. Inparticular there is disclosed herein an improved system for rapidlyclamping documents from a vacuum transporting position to an imagingposition (flattened against the platen) and unclamping the documentsinto a vacuum transporting position, which overcomes difficulties causedby the vacuum system and maintains control of the documents. There isalso disclosed here an improved vacuum belt document transport system,with an improved manifolding system of applying vacuum documentretention in a multibelt over-platen vacuum document transport system.

A particular problem with modern copiers with short conjugate optics ismaintaining the document being copied sufficiently flat on the imagingplaten to avoid optical distortion and to maintain all of the documentin focus. This is particularly difficult to compatibly combine withmaintaining positional control over the document, especially whenrapidly replacing the document with another document to be copied.

The vacuum belt document transport system disclosed herein represents animprovement over the multibelt over-platen vacuum document transport andmanifolding system of applying vacuum for document retention thereto ofXerox Corporation U.S. Pat. No. 4,618,138 issued Oct. 21, 1986 to MortonSilverberg. Also particularly noted thereon is Xerox Corporation U.S.Pat. No. 4,294,540 issued Oct. 13, 1981 to R. R. Thettu, although thatis a single belt system. Other vacuum aperture/groove patterns in adocument transport are disclosed in U.S. Pat. No. 4,544,265 issued Oct.1, 1985 to E. A. Powers, and Eastman Kodak U.S. Pat. No. 4,412,738issued Nov. 1, 1983 to D. K. Ahern, et al.

The disclosed system of clamping documents from a transporting positionto an imaging position against the platen, and unclamping the documentsinto a transporting position, is an improvement over various suchsystems disclosed in prior patents, of which Xerox Corporation U.S. Pat.No. 4,462,527 issued July 31, 1984 to T. N. Taylor et al is ofparticular interest as disclosing a non-uniform or variable spacingclamp lifting system, as particularly shown in FIGS. 6-8 thereof and itsdescription in Col. 12 lines 35-56, inter alia. As noted there and shownin FIG. 8, the clamp is lifted less near the rear of the platen (therear document side path guide) by the two different cams of FIGS. 6 and7. Note also Col. 12 lines 10-14, Col. 13 lines 47-55 and Col. 15 lines14-46. Tilted lifting of the platen clamp in this reference is describedas for a different reason-to prevent a document from climbing over therear registration edge by keeping that side of that clamp lower. Also,it does not show either belt transport or vacuum control of a document.It shows a frictional and feed wheel document transport with documentslippage for registration.

Other document clamping systems for document transports are disclosed inthe following patents. They disclose other copier document platentransports in document handlers or feeders in which there is a clampingplate which automatically moves down to flatten the document against theplaten for copying, and provide an imaging background surface, and thenlifts away to allow document feeding. This art includes XeroxCorporation U.S. Pat. No. 3,888,585 issued June 10, 1975 to T. R. Cross[see esp. FIGS. 6 & 7, and Col. 7, line 39 through Col. 8, line 21];U.S.Pat. No.4,335,954 issued June 22, 1982 to R. L. Phelps [see esp. FIG. 11& Cols. 9-10]; U.S. Pat. No. 3,944,366 issued Mar. 16, 1976 to D. A.Robertson; and U.S. Pat. No. 3,623,806 issued J. M. Short. They disclosevarious mechanisms for flattening a document original in relation to aplaten. However, many of these also disclose clamps with large wheelapertures, through which feed wheels extend, not belts, and makingundesirable holes in the imaging background surface which can cause copyprintout defects.

The above U.S. Pat. No. 4,335,954 patent to R. L. Phelps is also ofinterest as noting at the top of Col. 10 the problem of the vacuumcreated when the clamp rises. This is addressed there by slots orgrooves 190 in in the clamp plate surface preventing all the air frombeing squeezed out from under the clamp to try to keep the copy on theplaten surface after the cam-lifted unclamping. (The opposite of thepresent system.)

Also noted is an assumed Japanese publication "Koukai Gihoh" No. 87-1432reportedly published by Fuji Xerox Corp. (their No. FX 19058) on Feb.20, 1987 in Japan. It discloses a solinoid lifted pressure platepressing on the inside of a single unapertured document feeding beltover a platen when the belt is stopped. Noted as well is Fuji XeroxCorp. No. FX 16616 Japanese application No. P 60-161752 by K. Yamazakiwhich was reportedly filed on July 24, 1985 and laid open on Feb. 5,1987 as Laid Open No. 62-27256. It discloses an eccentric cam drivenmechanism for raising and lowering a plural belt document feeder copierplaten transport, to press the document against the platen duringcopying. There is no apparent disclosure of any vacuum system, ornon-uniform lifting or clamping.

U.S. Pat. No. 4,592,652 issued June 3, 1986 to K. Henmi, et al, is notedfor a movable copier platen clamp, noting especially FIG. 7 whichdiscloses a vacuum and eccentric lifting cams. However, no documenttransport is provided.

Other background references from other clamp applications include U.S.Pat. Nos. 4,029,404; 4,040,615; and 4,544,265.

In the document clamping system disclosed here, in contrast, an entirevacuum manifold unit is movably mounted above, and carrying, a set ofvacuum belts and also pushes them down to clamp a document. Thedisclosed system relates to clamping and unclamping a vacuum belttransport system. It teaches automatic clamping and unclamping of anentire vacuum manifold/belt unit for each document being fed by theplaten transport. The disclosed system maintains the document on avacuum transport and lifts it away from the platen during unclamping todo so. It has been known in the copier art for many years that a rapidopening of even a simple platen cover can lift a document off of theplaten, but this has been considered undesirable, and likely to losecontrol of it, and the normal solution has been to try to keep thedocument down on the platen, as noted above, not lifted with the platencover.

Transporting documents over the platen spaced above the platen glass, ashere, is desirable to avoid static generation and attraction to theglass. It also avoids abrasion of any anti-static conductive coatings onthe platen glass.

As xerographic and other copiers increase in speed, and become moreautomatic, it is increasingly important to provide higher speed yet morereliable and more automatic handling of the document sheets beingcopied, i.e. the input to the copier. It is desirable to feed,accurately register, and copy document sheets of a variety or mixture ofsizes, types, weights, materials, conditions and susceptibility todamage, yet with minimal document jamming, wear or damage by thedocument transporting and registration apparatus, even if the samedocuments are automatically fed and registered repeatedly, as forrecirculating document set precollation copying.

The art of original document sheet handling for copiers has beenintensively pursued in recent years. Various systems have been providedfor automatic or semiautomatic feeding of document sheets to and overthe imaging station of the copier for copying. The documents arenormally fed over the surface of an imaging station comprising atransparent platen, into a registered copying position on the platen,and then off the platen. Such automatic or semiautomatic documenthandlers eliminate the need for the operator to place and align eachdocument on the platen by hand. This is a highly desirable feature forcopiers. Document handlers can automatically feed documents as fast asthey can be copied, which cannot be done manually with higher speedcopiers, thus enabling the full utilization or productivity of higherspeed copiers.

A preferable document handling system is one that utilizes an existingor generally conventional copier optical imaging system, including theexternal transparent copying window (known as the platen or imagingstation) of the copier. It is also desirable that the document handlingsystem be readily removable, as by pivoting away, to alternatively allowthe copier operator to conventionally manually place documents,including books, on the same copying platen.

Although faster, more accurate, and automatic feeding into andregistration of each document at the correct position on the platen tobe copied is highly desired, this is difficult to accomplish withoutdocument jams or skewing (rotating) the document and/or damaging theedge of the document, particularly as it is being stopped. One problemis that documents can vary widely in sheet size, weight, thickness,material, condition, humidity, age, etc.. Documents may even have curls,wrinkles, tears, "dog-ears", cut-outs, overlays, tape, paste-ups,punched holes, staples, adhesive or slippery areas, or otherirregularities. Unlike sets of copy sheets, which generally are all fromthe same new clean batches and therefore of almost exactly the samecondition and size, documents often vary considerably even if they areall of the same "standard" size, (e.g. letter size, legal size, A4, B4,etc.). In contrast, documents even in the same set may have come fromcompletely different paper batches or have variably changed size withdifferent age or humidity conditions, etc.. Furthermore, the images ondocuments and their fusing can change the sheet feeding characteristicsand these images may be subject to damage in feeding if not properlyhandled, e.g. smearing of fresh typewriting ink. Yet it is desirable toautomatically or semiautomatically rapidly feed, register and copy evena mixture of sizes, types, and conditions of documents without documentjams or document damage and with each document correctly and accuratelyaligned to a desired registration position.

One of the most difficult to achieve features for automatic documenthandling is the rapid, accurate, reliable, and safe registration of eachdocument at the proper position for copying. Conventionally the documentis desirably either center registered or corner registered (depending onthe copier) by the document handler automatically at a presetregistration position relative to the copier platen. At thisregistration position two orthogonal edges of the document are alignedwith two physical or positional (imaginary) registration lines of thecopier platen at which the original document is properly aligned withthe copier optics and copy sheet/photoreceptor registration system forcorrect image transfer of the document image to the photoreceptor andthen to the copy sheet. This registration accuracy is desirablyconsistently within approximately one millimeter. If the document is notproperly registered, then undesirable dark borders and/or edge shadowimages may appear on the ensuing copy sheet, or information near an edgeof the document may be lost, i.e. not copied onto the copy sheet.Document misregistration, especially skewing, can also adversely affectfurther feeding and/or restacking of the documents.

In preferred types of copying systems the document is registered forcopying overlying a selected portion of full sized (full frame) platenwhich is at least as large as the largest document to be normally copiedautomatically. In such systems the document is preferably either scannedor flashed while it is held stationary on the platen in the desiredregistration position. That is, in these full frame systems the documentis preferably registered by being stopped and held during imaging at apreset position over the platen glass which is adjacent one side or edgethereof.

As shown in the art, and further discussed below, document handlingsystems have been provided with various document transports to move thedocuments over the copier platen and into registration. Such documentplaten transports may comprise single or plural transport belts or feedwheels, utilizing frictional and/or vacuum sheet driving forces. Variouscombinations of such transports are known with various registrationdevices or systems. Preferably the same platen transport sheet feeder isused to drive a document onto and off of the platen before and aftercopying as well as registering the document.

The cited art shows several approaches to registering a document forcopying at an appropriate position relative to the transparent copyingwindow. Typically the document is registered on one axis by driving itwith a platen transport against a mechanical gate or stop positionedtemporarily or permanently at or adjacent one edge of the platen. Thisis often at or closely adjacent the downstream edge of the platen. Thatallows unidirectional movement of the document across the platen,entering from the upstream side or edge closely following the proceedingdocument and ejecting after copying from the downstream side or edge ofthe platen. The registration gate or stop may comprise projectingaligned fingers, or roller nips, or a single vertical surface along oneregistration line, against which an edge of the sheet, preferably theleading edge, is driven into abutment to mechanically stop and therebyregister the sheet on one axis, in its principal direction of movement.Another function of such mechanical registration is to also deskew thedocument, i.e., to properly rotate and align it with this registrationline as well as to determine and control its registration position.However, such a mechanical gate cannot be interposed in the path of acontinuous web document and thus cannot be used for intermediateregistration thereof. Also it can sometimes damage the lead edge of adocument.

Document registration can desirably be done without mechanical documentstops on the platen, as disclosed for example in U.S. Pat. Nos.4,043,665 issued Aug. 23, 1977 to J. R. Caldwell; 4,132,401 issued Jan.2, 1979 to J. F. Gauranski, et al; or 4,295,737 or 4,391,505 issued Oct.20, 1981 and July 5, 1983 to Morton Silverberg,. This can be done bypreregistering the document to a platen transport belt and then movingthe document a known, preset, distance over the platen on the belt intoregistration, providing there is no slippage during this entire movementbetween the document and the belt. Alternatively, this can be done bysensing, on the platen or upstream of the platen, with a document edgesensor, an edge of a document being transported onto the platen. Thedocument is fed over the platen with a non-slip transport driven by aservo-motor or steppermotor which is stopped after a preset time periodor movement to stop the document on the platen in the desiredregistration position. Such a measured-stop registration system, for anRDH, is taught in U.S. Pat. No. 4,579,444 issued Apr. 1, 1986 to T. S.Pinckney and H. J. Sanchez (D/84074), and references cited therein.

In some document handling systems a system for also side registering(laterally positioning) the document on the platen is used, i.e.aligning the original on both axes while on the platen, e.g. U.S. Pat.No. 4,411,418 or 4,335,954. However two axes on-platen registration isnot required, and such lateral or second axis registration may be doneupstream of the platen, as by confinement of the documents within theside guides in the document tray from which the documents are fed, ordriving the sheet against a side guide, e.g. U.S. Pat. Nos. 4,257,587;4,266,762 or 4,381,893.

In the description herein the term "document" or "sheet" refers to ausually flimsy sheet of paper, plastic, or other such conventionalindividual image substrate, and not to microfilm or electronic imageswhich are generally much easier to manipulate. It is important todistinguish electronic copying systems, such as the Xerox "9700"printer, which read and store images of documents electronically andcreate copies by writing on a photoreceptor with a laser beam, or thelike, since they do not have the problems dealt with here.

The "document" here is the sheet (original or previous copy) beingcopied in the copier onto the outputted "copy sheet", or "copy". Relatedplural sheets of documents or copies are referred to as a "set". A"simplex" document or copy sheet is one having an image and "page" ononly one side or face of the sheet, whereas a "duplex" document or copysheet has a "page", and normally an image, on both sides.

The present invention is particularly suitable for precollation copying,i.e. automatically plurally recirculated document set copying providedby a recirculating document handling system or "RDH". However, it alsohas applicability to nonprecollation, or postcollation, copying, such aspostcollation operation of an RDH or semiautomatic document handling(SADH) as discussed above. Postcollation copying, or even manualdocument placement, is desirable in certain copying situations, evenwith an RDH, to minimize document handling, particularly for delicate,valuable, thick or irregular documents, or for a very large number ofcopy sets. Thus, it is desirable that a document handler for aprecollation copying system be compatible with, and alternatively usablefor, postcollation and manual copying as well.

Some examples of Xerox Corporation RDH are U.S. Pat. Nos. 4,459,013issued July 10, 1984 to T. J. Hamlin et al; 4,278,344 issued July 14,1981 to R. B. Sahay; and 4,579,444, 325 or 326. Some other examples ofrecirculating document handlers are disclosed in U.S. Pat. Nos.4,076,408; 4,176,945; 4,428,667; 4,330,197; 4,466,733 and 4,544,148. Apreferred vacuum corrugating feeder air knife, and a tray, for an RDH,are disclosed in U.S. Pat. Nos. 4,418,905 and 4,462,586. An integralsemi-automatic and computer form feeder (SADH/CFF), which may be anintegral part of an RDH, as noted in Col. 2, paragraph 2, therein, isdisclosed in U.S. Pat. No. 4,462,527. Various others of these patents,such as U.S. Pat. No. 4,176,945 above, issued Dec. 4, 1979 to R.Holzhauser (Kodak) teach plural mode, e.g. RDH/SADH, document handlers.

The present invention overcomes various of the above-discussed problems,and provides various of the above features and advantages.

A feature of the specific embodiment disclosed herein is to provide, adocument handler for presenting documents to the platen of a copier forcopying, comprising a vacuum belt platen transport system for feedingthe documents over the platen and into an imaging position over theplaten, wherein said vacuum belt platen transport system comprisesplural document transporting belts movable under a substantially planarvacuum plenum backing and imaging background surface overlying saidplaten, and vacuum means for applying a partial vacuum to a documentsheet being transported by said movable belts over said platen, andmeans for moving said belts, the improvement comprising clamping meansfor moving said vacuum plenum backing and imaging background surfaceagainst said platen to flatten said belts and a document thereon againstsaid platen for copying said document, said clamping means includingunclamping means for lifting said vacuum plenum backing and imagingbackground surface slightly away from said platen while supplying saidpartial vacuum with said vacuum means to lift a document away from saidplaten retained on said belts, for transporting a document with saidbelts, said unclamping means including means for lifting a first side ofsaid vacuum plenum backing and imaging surface up away from said platensubstantially before the opposite side thereof, and then subsequentlylifting said opposite side, to generate a controlled air flow forassisting in retaining the document to said belts as said vacuum plenumbacking and imaging surface is lifted away from said platen, said meansfor moving said belts being operable when said vacuum plenum backing andimaging surface is lifted away from said platen and while supplying saidpartial vacuum with said vacuum means to retain a document against saidbelts.

Further features provided by the system disclosed herein, individuallyor in combination, include those wherein said clamping and unclampingmeans comprises plural cams with different cam rise times connected viacam lifters to lift said first side of said vacuum plenum backing andimaging surface with a different motion than said opposite side by saidcams being rotatably driven for clamping and unclamping; wherein saidclamping means moves down said first side of said vacuum plenum backingand imaging surface towards said platen beginning slightly before movingdown said opposite side of said vacuum plenum backing and imagingsurface towards said platen, to generate a controlled air flow expulsionof air out from under said vacuum plenum backing and imaging surfaceduring clamping; wherein said clamping means moves down said first sideof said vacuum plenum backing and imaging surface towards said platenbeginning approximately 5 milliseconds before moving down said oppositeside, with further rotation of said same cams, but beginning saidmovement of said first side before said opposite side with differentsaid cam rise times configurations of said cams, to generate acontrolled air flow expulsion of air out from under said vacuum plenumbacking and imaging surface during clamping; wherein said unclampingmeans, with said rotation of said cams, first lifts said first side ofsaid vacuum plenum backing and imaging surface about 2.5 mm away fromsaid platen while said opposite side remains down in contact with theplaten, and then lifts said opposite side about 0.8 mm, and then saidvacuum plenum backing and imaging surface is leveled by lifting saidopposite side from said about 0.8 mm to about 1.75 mm, and, atapproximately the same time, said first side is dropped from said about2.5 mm to about 1.75 mm; wherein clamping and unclamping is accomplishedby common rotation of said cams with different cam profiles providingsaid different cam rise times, and wherein after said unclamping is atleast partially completed a document previously copied is ejected bysaid platen transport system and a next document is brought over theplaten by said platen transport system, while maintaining said vacuumretention of the documents, and then before the copying of this nextdocument it is clamped against the platen by moving down both said firstside and said opposite side of said vacuum plenum backing and imagingsurface with further rotation of the same cams but beginning themovement of said first side a fraction of a second before the movementof said opposite side to move said surface down at an angle towards saidplaten which squeeges out air from under the document before the finalclamping, in which both said first and said opposite sides are flattenedagainst said platen; and wherein additional vacuum retention meansconnecting with said vacuum means are provided along said first edge ofsaid vacuum plenum backing and imaging surface to provide asubstantially higher partial vacuum holding force to the edge area of adocument overlying said first edge for resisting stripping of thedocument from said vacuum belt platen transport during said unclampinglifting movement.

Further disclosed features include a copying method utilizing a documenthandler for presenting documents to the platen of a copier for copying,comprising a vacuum belt platen transport system for feeding thedocuments over the platen and into an imaging position over the platen,wherein said vacuum belt platen transport system comprises pluraldocument transporting belts movable under a substantially planar vacuumplenum backing and imaging background surface overlying said platen, andvacuum means for applying a partial vacuum to a document sheet beingtransported by said movable belts over the platen, and means for movingsaid belts, comprising the steps of:

clamping said vacuum plenum backing and imaging background surfaceagainst the platen to flatten said belts and a document thereon againstthe platen for copying said document by unevenly moving said vacuumplenum backing and imaging background surface and said belts downtowards said platen,

unclamping said vacuum plenum backing and imaging background surface andsaid belts and a document thereon from said platen by unevenly liftingsaid surface away from said platen while supplying a partial vacuum withsaid vacuum means to lift a document away from said platen retained onsaid belts,

said unclamping including lifting a first side of said vacuum plenumbacking and imaging surface up away from said platen substantiallybefore the opposite side thereof, and then subsequently lifting saidopposite side, to generate a controlled air flow for assisting inretaining the document to said belts as said vacuum plenum backing andimaging surface is lifted away from said platen,

and transporting a document with movement of said belts and with saidpartial vacuum retaining a document against said belts after saidunclamping is at least partially completed.

Additional features, individually or in combination include thosewherein said clamping moves down said first side of said vacuum plenumbacking and imaging surface towards said platen beginning slightlybefore moving down said opposite side of said vacuum plenum backing andimaging surface towards said platen, to generate a controlled air flowexpulsion of air out from under said vacuum plenum backing and imagingsurface during clamping; wherein said unclamping first lifts said firstside of said vacuum plenum backing and imaging surface about 2.5 mm awayfrom said platen while said opposite side remains down in contact withsaid platen, and then lifts said opposite side about 0.8 mm, and thensaid vacuum plenum backing and imaging surface is leveled by liftingsaid opposite side from said about 0.8 mm to about 1.75 mm, and, atapproximately the same time, said first side is dropped from said about2.5 mm to about 1.75 mm; wherein said clamping and unclamping isaccomplished by rotation of cams with different cam profiles, andwherein after said unclamping is at least partially completed a documentpreviously copied is ejected by said platen transport system and a nextdocument is brought over the platen by said platen transport system,while maintaining said vacuum retention of the documents, and thenbefore the copying of this next document it is clamped against theplaten by moving down both said first side and said opposite side ofsaid vacuum plenum backing and imaging surface with further rotation ofthe same cams but beginning the movement of said first side slightlybefore said opposite side to move said surface down at an angle towardssaid platen which squeegees out air from under the document before thefinal clamping, in which both said first and said opposite sides areflattened against said platen.

Some examples of various other prior art copiers with document handlers,and especially with control systems therefor, including document sheetdetecting switches, etc., are disclosed in U.S. Pat. Nos.: 4,054,380;4,062,061; 4,076,408; 4,078,787; 4,099,860; 4,125,325; 4,132,401;4,144,550; 4,158,500; 4,176,945; 4,179,215; 4,229,101; 4,278,344;4,284,270, and 4,475,156. It is well known in this art, and in general,how to program and execute document handler and copier control functionsand logic with conventional or simple software instructions forconventional microprocessors. This is taught by the above and otherpatents and various commercial copiers. Such software may vary dependingon the particular function and particular microprocessor ormicrocomputer system utilized, of course, but will be available to, orreadily programmable by those skilled in the applicable arts withoutexperimentation from either descriptions or prior knowledge of thedesired functions together with general knowledge in the generalsoftware and computer arts. It is also known that conventional orspecified document handling functions and controls may be alternativelyconventionally provided utilizing various other known or suitable logicor switching systems.

All references cited in this specification, and their references, areincorporated by reference herein where appropriate for appropriateteachings of additional or alternative details, features, and/ortechnical background.

Various of the above-mentioned and further features and advantages willbe apparent from the specific apparatus and its operation described inthe example below. The present invention will be better understood byreference to this description of this embodiment thereof, including thedrawing figures (approximately to scale), wherein:

FIG. 1 is a side view of an exemplary recirculating but plural modedocument handler for a copier, as shown in the cross-referencedapplication, in which the system of the invention may be incorporated asshown in the other Figures;

FIG. 2 is a partial side view of the document handler of FIG. 1illustrating the clamping and unclamping system of the platen vacuumbelt transport;

FIG. 3 is a bottom view of the platen transport of the document handlerof FIGS. 1 and 2 with the belts shown partially broken away to betterillustrate the underlying vacuum manifold surface grooves and matingapertures patterns with relation to the overlying document transportbelts;

FIGS. 4 and 4A respectively show enlargements of the profiles of thefront and rear lifting cams of the clamping and unclamping systemillustrated in FIGS. 2 and 5;

FIG. 5 is a schematic partial top view of the clamping and unclampingsystem of FIG. 2, further illusrating the operation of the cams shown inFIGS. 4 and 4A; and FIG. 6 is an enlarged partial cross-sectional viewof the rear registration edge area of the platen transport vacuummanifold surface and belts of FIG. 3 (Note that this Figure is "upsidedown" from the actual orientation because FIG. 3 is a bottom view.)

Describing now in further detail the example illustrated in the Figures,there is partially schematically shown in FIG. 1 an exemplary copier 10,with an exemplary document handling system 20 (preferably a plural modeRDH, to be described herein). The copier 10 may be of any known type,such as those disclosed in above-cited copier patents. The exemplary DH20 illustrated here is similar to that shown in the abovecross-referenced U.S. Ser. No. 029,027, or the generally comparabledisclosures in U.S. Ser. No. 029,026, both filed Mar. 23, 1987. Howeverthe system disclosed herein is applicable to various other DH's, such asthose shown in various above-cited patents thereon. As shown therein, itis previously known to have two separate document inputs, arecirculating or RDH input stacking tray 21, and a side entrance 22 forsemiautomatic document handling (SADH), into which documents may beindividually inserted by the operator, sequentially and/or in anoperator selected "job interrupt" mode.

The RDH 20 provides for automatically transporting individual registeredand spaced document sheets onto and over the conventional platen imagingstation 23 of the copier 10, using a vacuum belt platen transport system32 overlying the platen 23. Documents are inputted to one end of theplaten transport 32 either from the RDH input provided by the restackingtray 21 on top of the unit, spaced above the platen, or from theseparate document input 22 directly adjacent one side of the platen,shown at the right side here.

As is conventionally practiced, the entire document handler unit 20pivotally mounts to the copier 10 so as to be liftable by the operatorup away from the platen for manual document placement and copying or jamclearance of documents jammed in the platen area. The DH 20 hasconventional external covers (not shown, for drawing clarity).

Other than the DH 20 system modifications and controls and otherfeatures to be described herein, the exemplary copier 10 may be, forexample, the well known "Xerox" "1075" or "1090" or any otherxerographic or other copier, as illustrated and described in variouspatents cited above and otherwise, including U.S. Pat. No. 4,278,344 andothers. The exemplary copier 10 may conventionally include aphotoreceptor belt 12 and the conventional xerographic stations actingthereon for respectively charging, image exposing at 14, imagedeveloping, etc.. Documents on the platen 23 may be imaged onto thephotoreceptor 12 at area 14 through a variable reduction ratio opticalimaging system 16 to fit the document images to the selected size ofcopy sheets. The copier 10 is preferably adapted in a known manner toprovide duplex or simplex precollated or postcollated copy sets fromeither duplex or simplex original documents copied from the RHD 20.

The control of all sheet feeding is, conventionally, by the machinecontroller 100. The controller 100 is preferably a known programmablemicroprocessor, exemplified by the previously cited art. The controller100 conventionally controls all of the machine steps and functionsdescribed herein including the operation of the document feeder 20, thedocument and copy sheet gates, the feeder drives, etc.. As furthertaught in those references, the controller 100 also conventionallyprovides for storage and comparison of the counts of the copy sheets,the number of documents recirculated in a document set, the desirednumber of copy sets and other selections by the operator through thepanel of switches thereon, time delays, jam correction control, etc..The controller 100 may be conventionally connected to receive jam andcontrol signals from various conventional document sheet sensors mountedin the document recirculation path of the RDH, including those shown inthe respective locations shown here in the Figure, including 39, 52, 55,56, and 57.

Referring further to the exemplary plural mode document handling system20 illustrated in FIG. 1, documents may be fed to the same platen 23 andplaten transport 32 input position from either the SADH input 22, orfrom the RDH tray 21. The latter input is through an RDH input path 24between that tray 21 and the upstream end of the the platen transport32, preferably including, as shown, a known stack feeder/separator, asensor 52, and a first set of turn baffles and feed rollers to invertthe documents before copying. The SADH input 22 may conventionallyinclude a tray and edge guide and sensors and an SADH preregistrationgate 30. This gate 30 may have any of the various configurations andoperating mechanisms illustrated in various of the above-noted prior artreferences on registration gate systems. The gate 30 illustrated here ispreferably retractable in and out of the SADH input path to the platenfrom the SADH input 22 by solenoid actuation controlled by thecontroller 100. The SADH input path feeds in documents directly to theplaten, without inversion, and bypassing, without interference, the RDHinput path 24, so that the two inputs can automatically operate in aselected interleaved or interrupt feeding sequence.

The SADH input 22 here preferably also includes slightly skewedcross-rollers 26. As taught in the above-cited U.S. Pat. No. 4,579,444,these provide side edge registration towards a rear edge guide at thisinput, as well as feeding of the document forward for registration anddeskewing against the gate 30. Such cross-rollers may also be providedin the RDH input path 24. Just downstream of the gate 30 are take-awayor on-platen rollers 28 providing a document sheet feeding nip forengaging and transporting any document sheet which is past the gate 30or the RDH input path 24. The rollers 28 feed the documents directlypast sensor 28 into the input to the platen transport system 32.

The platen transport system 32 here comprises a vacuum manifold 33 forholding documents against plural belts 35 engaging and transporting thedocuments without slippage over the platen 23 into the desiredregistration position, of the general type disclosed in the above-citedU.S. Pat. No. 4,618,138. The platen transport system 32 and the rollers28 may be incrementally servo motor driven by the controller 100 in amanner taught by various of the above-cited references.

After the documents are copied on the platen 23, they are, in thisexample, ejected by the platen transport system 32 into downstream oroff-platen rollers 34 and fed past a gravity gate 37 and sensor 39 to adecision gate 36. If the gate 36 is up (it always is for CF or normalSADH copying) it deflects the documents directly to an SADH documentoutput including output rollers 38. If the decision gate 36 is down, asfor RDH, and for job recovery here, sheet documents are deflected intoan RDH return path 40, past sensor 55. However, this RDH return path 40includes reversible rollers 42 to provide a choice of two return pathsto the RDH tray 21; a simplex return path 44 with an inversion, or aduplex return path 46 without an inversion. For the duplex path 46 therollers 42 are reversed to reverse feed the previous trail edge of thesheet back to the now-dropped gate 37 which now deflects that sheet intothe path 46. The duplex return path 46 provides a desired circulationinversion of duplex documents, as returned to the tray 21, for copyingtheir opposite sides in a subsequent circulation, or circulations, asdescribed in the above-cited art. This is because a duplex documentreturned through the duplex return path 46 has only one inversion percirculation (in the RDH input path 24). In contrast, in the completesimplex circulation path there are two inversions per circulation, onein each of the paths 24 and 44, which equals no inversion percirculation. Thus, simplex documents are always returned to tray 21 intheir original, face up, orientation.

As illustrated, the RDH tray 21 here also includes a variable positionrear registration edge or backstop, illustrated here with several dashedlines, for initially accommodating and restacking various sizes ofdocuments. The illustrated DH system 20 utilizes for its RDH feeding aknown combined corrugated vacuum feeding and air knife separator systemfor feeding out sequentially the bottom-most sheet of the stack in thetray 21, as described in various of the above-cited references.

For normal cut sheet SADH input 22 document feeding in the DH system 20,the documents are fed and controlled by, in order, the cross-rollers 26,the nips of the on-roll rollers 28, the platen vacuum belt transport 32,the nips of the downstream or off-roll rollers 34, and then the nips ofthe output or exit roll rollers 38. For RDH circulation the sheets areadditionally driven and controlled by the stack feeder/separator and therollers and curved baffles in the paths 24 and 44 or 46, and the ejectrollers at the restack entrance at the rear of the tray 21, asillustrated. Individual sheets are "handed off" from one feeding nip toanother along the document path with very restricted slippage to ensurepositive and registered feeding.

In the system illustrated here, the portions of all the roller pairunits 26, 28, 34 and 38 which are below the document path are idlerrollers mounted to the body of the copier. All the above-path rollers ineach of these nip pairs are driven rollers, and all of those are mountedto the pivotal platen cover unit of the DH system 20. Thus, theseabove-path rollers may all be lifted up, away from the platen 23, toexpose it and to open all these roller nips and the platen transport 32.

Turning now to details of the exemplary system disclosed herein, thereis disclosed an improved platen transport system for copier, withfeatures as previously described above in the introduction. The clampingand unclamping system disclosed here overcomes particularly difficultdocument handling problem in modern copiers with short conjugate opticsproviding a narrow depth of field calling for reliable documentflattening against the platen with a very planar clamping surface, yetbeing compatible with high speed document handlers requiring rapiddocument platen exchange times. That is especially critical anddifficult with vacuum transports, as discussed further herein.

Here, as the clamp lifts, the inrush of air is controlled so as not tostrip the sheet from the vacuum platen transport 32, and preferably tohelp lift and hold the sheet against the transport 32 instead. This isprovided by lifting the clamp first at the registration edge, where thesheet is controlled. As this first edge lifts, inrushing air assists inlifting the rest of the sheet. Here, as the clamp closes, the clampingpushes the entire platen transport 32, and therefore the document heldon it, towards the platen glass at an angle, pushing air aside. Clampingand unclamping can be achieved in 120 milliseconds or less with thissystem yet maintain document control.

As noted, most of the above references teach clamps with aperturesthrough which feed wheels extend, making undesirable holes in theimaging background surface which can show up as black areas on the copysheets, and clearly being unsuitable either for a vacuum or a beltsystem.

The moving clamp system here includes the external integral bottomsurface 33a of an entire moving vacuum manifold 33 above a set of belts35, which surface 33a pushes the belts 35 down against the document forclamping. l.e. the entire vacuum belt feeder unit 32, including themanifold 33, its surface 33a, the belts 35 and their mounting frame androllers, etc. moves up and down relative to the platen to provideautomatic clamping and unclamping. The belts 35 press the document flatagainst the platen 23 because the surface 33a underlying them holds thebelts flat. As will be described, the document lifting movement requiredfor the unclamping is difficult to achieve here because the clamp islifting against the vacuum forces formed between the sheet and theplaten glass. This vacuum is formed as a result of greatly increasingthe volume between them during lifting.

The bottom or clamping surface 33a is generally planar, but channeled orgrooved 54, and apertured 53 into the manifold or plenum 33 interior,for vacuum application to the document in the gaps 35a between the belts35, as will be described. The frame of the manifold unit 33 here alsoprovides belt supports, such as those further described in theabove-cited U.S. Pat. No. 4,618,138 issued Oct. 21, 1986 to M.Silverberg. The clamping surface 33a also preferably has a preset,preformed, concave "bow", to assist or insure flattening, of about 1 mm(millimeter) to 0.5 mm when not engaged. That is, the unstressed(unclamped) surface 33a preferably has a large radius concave "belly",with the center of surface 33a about 0.5-1.0 mm further away from theplaten than the outer edges of surface 33a, to insure that this surface33a presses flat against the platen. That is assisted by the illustratedsprings 70 pressing down the outer corners of the frame holding themanifold 33 against the platen, except when the clamp is lifted. Thatis, the unit 32 is spring-loaded down. The "bow" also helps insuremaximum document flattening at the document edges, where it is mostoptically sensitive. This "bow" or "belly" centerline is preferablyapproximately alligned with the centerline of the lens system wheredocument spacing and distortion is the least sensitive. Also, it helpsprovide for a small volume of air during clamping between the documentsheet and the glass to aid document unclamping by reducing vacuumholddown forces.

As shown in FIGS. 2 and 5, the unit 32 is lifted up against the springforce by lifting 4 cam followers 64 by rotation of 2 pairs of cams 60,60a and 62, 62a, on two fixed camshafts 66, 67, which are servo driven,to provide the following unique movements to overcome the vacuum/airflow problems: First the rear or side registration edge of the clampsurface 33a is lifted by the rear cams 62, 62a by about 0.1 inch (2.5mm), to allow air to get under the clamp there first. Then the frontcams 60, 60a lift the front or operator side of the clamp (the sideopposite the redge edge) up by about 0.03 inch (0.8 mm). Then the belts35 drive may be started, and the rear edge is dropped down by the rearcams from said 2.5 mm to about 1.75 mm while raising the front edge fromsaid 0.8 mm to said 1.75 mm to level it. Note the document sheet feedingmay be started during this special small but irregular unclampingmovement of the clamp.

The configurations or profiles of the two identical front cams 60, 60aare shown in FIG. 4, and those of the two identical rear cams 62, 62aare shown in FIG. 4A. FIGS. 2 and 5 show how these four cams move theircam followers 64, which directly translate the varying cam profiles intoan equal movement of the entire platen transport unit 32. All the camsmay be commonly rotated at the same velocity and by the same rotationangle between two common (dashed Line) dwell angles for the final up anddown (unclamped and clamped) positions. The clamping position is notcritical for the cams because the springs 70 and gravity can do theactual or final clamping. The radii of all the cams at the two dwellpoints for the clamped and unclamped positions may be the same, but theintervening profiles of the rear cams differ substantially from those ofthe front cams, as shown in FIG. 4 vs FIG. 4A. There may be less thanapproximately 2.6 mm between the largest and smallest radii of theexemplary cams here. That represents the maximum possible differencebetween the raised and lowered positions of the lower surface 33a forthese cams in this configuration. Note, however, that the angularpositions at which the rear cams reach their maximum radius is verydifferent from that of the front cams. l.e., the cam rise and fall isvery different for the front cams vs. the rear cams.

As the clamp lifts in this described manner, the surface 33a and thedocument sheet thereon "wave" upwardly from the rear or registrationedge, rather than lifting straight up uniformly. This provides adesirable and controlled airflow pattern as the clamp is lifted.

Cooperating therewith are additional vacuum grooves 58 and vacuumapertures 59 along the rear registration edge of the surface 33a. Noteparticularly FIG. 6. These additional apertures 59 and grooves 58increase the vacuum retention of that edge of the document against thetransport, resisting the airflow in that area as the clamp lifts. Notethat the pattern or spacing of the apertures 59 and their communicatingcorresponding channels or grooves 58 is denser, i.e. they are bothlarger and closer together than the other apertures 53 and grooves 54 onthe surface 33a. These rear edge grooves 58 are substantially deeper,e.g. approximately 8 times deeper, so as to apply a much higher vacuumforce to this rear registration edge of the document between the lastbelt 35 on that side and the registration edge. Because these rear edgevacuum apertures 59 are much larger in diameter and closely spaced, theyare manufactured in the staggered pattern illustrated in FIG. 3 ratherthan arranged linearly as the other groups are.

Further noting FIG. 6, additionally provided along the rear orregistration edge of the surface 33a is a raised edge or rib seal 72extending along the rear edge of bottom plate 33a. The rib 72 height isapproximately the same as the belt 35 thickness. This rib seal 72 ispreferably approximately 0.25 mm high and 6 mm wide, and terminates andseals the outer ends of the edge grooves 58. Therefore a confined ordefined vacuum chamber is provided between the rear edge of the rearmostbelt 35 and this rib 72, forming a substantially higher intensity vacuumunder the outer edge of the document sheet. Note that the outer edge ofthe document is always overlying this high vacuum area and at leastpartially overlying the rib 72, because most documents fed by thisdocument handler 20 are registered to the rear registration edge, whichis directly over or immediately outside of the rib 72. That rearregistration edge is not physically present in the platen area here butmay be provided by pre-registering the rear edge of the document, to aline adjacent the outside edge of the rib 72, immediately upstream ofthe platen transport, by an edge registration guide provided in thedocument path there from both the RDH and SADH inputs, against which therear edge of the document may be driven by crossed rollers, as describedin the above cited patents. Thus, the rear edge of most sizes ofdocuments are always lying on and sealing this rib seal 72, not insidethereof, and not extending substantially beyond this rib 72. The rib 72also reduces document distortion at the top edge area where that is mostsensitive.

Alternatively to the plural additional vacuum grooves 58, a singleshallow flat bottomed channel (e.g., 4 mm wide by 0.5 mm deep, below therib 72) can be provided extending along and parallel to and just insidethe rib 72, i.e. extending in the direction of document motion, so as tobe closed by an overlying document. In FIG. 6 it could appearsubstantially the same as present FIG. 6 except that at reference 58 thesolid line would be where the lower dashed line is now.

It will also be noted that an additional groove or channel pattern 74may be provided at the front edge of the surface 33. However thesegrooves 74 are only functionally utilized in the case of very large(very long) documents which would extend out over these grooves 74.

As the clamp lifts in the manner described, the surface 33a and thedocument sheet thereon "wave" upwardly, starting from the rearregistration edge, rather than lifting straight up uniformly. The rearregistration edge of the document, which is held with extra vacuum forceas described above, is lifted first. The additional vacuum grooves 58and vacuum apertures 59 along the registration edge vacuum retain thedocument edge against any peeling or separating tendency caused by theairflow entering there as the clamp lifts. Note that it would beundesirable to apply such a large vacuum retention force for the entiredocument. That would have several disadvantages, including increaseddrag forces of the belt and document against the surface 33a, andpossible wrinkling of thin documents.

Turning now to the clamping operation and movement, this differsconsiderably from the above described unclamping movement, even thoughhere it is accomplished by further movement of the same cams. Forclamping, the extent and direction of motion of the front and rear edgesof the surface 33a may be the same, but preferably the rear orregistration edge starts to drop about 5 milliseconds before the frontedge. Thus an air squeegeeing action occurs during clamping, in whichair is squeezed out from under the clamp toward the front duringclamping. Thus the rear or registration edge will contact the platenfirst, although the movement of both the front and rear edges of thesurface 33a is decelerated before the platen is engaged. Both front andrear ends of the clamp can be moved down at about the same velocityuntil this deceleration occurs, shortly before the contact of the rearedge. Then after the rear edge contacts, the continued rotation of thecams flattens both the front and rear edges of the surface 33a withequal force against the platen. This wave or squeegeeing of the documentdown during the clamping movement helps to keep lightweight documentsfrom being wrinkled by the belt transport by overpressure by trapped airpockets under the document against which the thin document would beforced, i.e., localized undersired air pressure against the documentwhich could cause buckling or wrinkling of a thin document.

To summarize the motions during unclamping, the rear edge is firstlifted about 2.5 mm while the front edge remains down in contact withthe platen. Then the front edge is lifted to about 0.8 mm. Then thebelts may be started, since there is enough air available to provideadequate vacuum retention and therefore nonslip transport. Then theclamp is leveled by lifting the front edge from 0.8 mm to 1.75 mm and,at the same time, the rear edge is dropped from 2.5 mm to 1.75 mm. Thedocument previously copied is ejected by the platen transport and thenext document is brought over the platen by this platen transport,maintaining vacuum retention at all times. Then before the copying ofthis next document it is clamped against the platen by moving down bothfront and rear edges of surface 33a with further movement of the samecams but beginning the movement of the rear about 5 milliseconds beforethe front to move the clamp down at an angle which squeegees out airfrom under the document before the final clamping in which both edgesare against the platen.

To summarize the exemplary motion drive disclosed herein, as shown inFIGS. 2 and 5, the four cams are on two driven shafts mounted to theframe of the entire DH unit 20 and therefore rotating about fixed axiesin normal operation (ie, unless the entire DH 20 is lifted up from theplaten). The four conventional cam followers 64 are each positioneddirectly above the 4 cams, to be lifted in proportion to the cam profileor radii and angle of rotation. The cam followers 64 are fastened to arigid support frame fastened to and holding the vacuum plenum, andpreferably the belts. This movement from the cam profiles is therebytransmitted directly to the platen transport unit 32, including surface33a. In addition to gravity, the 4 springs 70 between the DH 20 frameand the frame of the platen transport unit 32 act to press the latterdown, and also hold the cam followers 64 down against the cams andassist rapid downward (clamping) acceleration. Note that this clampingand unclamping must occur at the document exchange rate, which is equalto or one-half of the full copying rate of the copier.

To hold the platen transport in position horizontally yet allow verticalunclamping movement relative to the cams and the cam shafts, there areillustrated here in FIG. 5 additional cylindrical bearings on the camshafts 66, 67, and mating confining bearing retainers on the unit 32allowing vertical movement but not horizontal movement. Mating pins,guides, slide plates or other retainers could be used.

Here, in a document feeder 20 for transporting document sheets over theplaten of a copier with a vacuum belt platen transport system 32 withmeans for stopping the document sheet at an imaging position on theplaten, the vacuum belt platen transport system 32 comprises pluralwhite opaque belts 35 moving under a white vacuum plenum backing surfaceoverlying the platen, and includes a conventional vacuum source forapplying a partial vacuum to a document sheet being transported by themoving belts. The belts 35 are preferably thin, low-frictional,non-elastomeric, plastic belts as in said U.S. Pat. No. 4,618,138, butnot translucent or transparent, because the belts 35 are opticallymasking vacuum holes 53 and 59 here. (Said U.S. Pat. No. 4,618,138 alsodisclosed white belts in Col. 9 lines 59-60.) The belts 35 areunapertured and the exposed area of the vacuum plenum clamping andbacking surface 33a is unapertured in the imaging position, so that thevacuum belt transport system is effectively invisible to the copier.That is, the apertures 53 here extend in rows over most of the surface33a, but only underlying the edges of belts 35.

As observed in various references, multiple belt transports have oftenhad very serious "printout" or copy defect problems with "show-around"and "show-through". "Show-through" is the printing out of dark areas onthe copy sheet because the copier optics "sees" dark areas on thedocument transport through the document, particularly through atransparent or very thin or otherwise translucent document."Show-around" can occur when the document is mis-registered, or areduction copy is being made, which directly exposes areas of the platentransport beyond (outside of) one or more edges of the original. Both ofthese types of copy defects are particularly likely with vacuum platentransports and plural belt platen transports, because the belt edges andvacuum apertures tend to have both printable edge shadows and dirtcontamination (visible darkening), particularly if such belts are of arelatively thick or high friction elastomeric material. This can producevery undesirable dark areas on the copy sheets.

Vacuum belt transports desirably provide a combination of non-criticalfrictional feeding by the belt(s) assisted by a partial vacuum appliedthrough apertures in the belt or between the belts to retain or pull thedocument or portions thereof against the belt(s), as taught in the citedart. However, vacuum belt transports have introduced serious additionalproblems of "show-around" and "show-through" copy defects. Undesirabledark background markings on the copy sheets can occur from images oflight absorbed in the vacuum apertures in or for the belt(s) or in theunderlying vacuum manifold or plenum surface for the belt(s).

The platen transport system 32 here includes a vacuum plenum or manifold33 having a novel white backing or imaging surface 33a closely overlyingthe platen 23, as will be further described. This plenum backing surface33a is closely overlayed with a plurality of driven transport belts 35,spaced apart by relatively narrower defined gaps 35a. The belts 35,spaced apart by relatively narrower defined gaps 35a. The belts 35 areeach relatively narrow endless loops. These belts 35 may be, forexample, uniformly made from a single layer of commercially availablepolyester material. They are preferably much less than 1/2 mm thick, anda thickness of only approximately 0.2 mm has been found to be operativeand desirable, as disclosed in the cited U.S. Pat. No. 4,618,138.

The lower or outer (document transporting) surface of the belts shouldbe sufficiently smooth so as to resist the accumulation of contaminantssuch as paper lint thereon, and so as to maintain the preferredinvisibility of the belts to the copier. If desired, some belt surfacetexturing may be provided for vaccum migration across the belt.

Vacuum is applied to the document in the transport system 32 via thesurface 33a in the gaps 35a between the belts. This vacuum holds adocument sheet against the belts 35 with sufficient force that the lowfriction engagement of the moving belts 35 against such avacuum-retained document provides an adequate transporting force. Thatis, sufficient normal force between the sheet and the belts 35 such thateven with the low coefficient of friction of the belts there issufficient forward transporting force to reliably transport the documentwith minimal slippage from the initial engagement of the documentupstream (off of) the platen, then across the platen towards thedownstream edge thereof, i.e., towards and into the forward edgeregistration position, and then to eject the document from the platenafter it has been registered and copied. The applied vacuum also helpsto retain or lift up the document sheet thereon out of substantialengagement with the platen during feeding (while unclamped), therebyreducing frictional resistance to feeding and static electricitygeneration between the document and the platen. (Conventional conductivebrush or pin coronode or other electrostatic discharge means may beprovided for the documents, the belts and/or the platen, if desired).

The conformable mounting of the platen transport system 32 over theplaten may be variously provided. As previously described, preferably,the entire platen transport system 32, comprising the vacuum plenum 33,its imaging surface 33a, the belts and their supports, and all of thecomponents directly attached thereto, are mounted for a slight butcontrolled independent movement relative to the rest of the documenthandling system 20, i.e., relative to the cover and the frames of the DHsystem 20 which support the platen transport system 32. It is mounted soas to be able to conform to the platen surface when clamping. Limitedaxially deformable coil springs 70 or the like may be provided at thefour corners of the upper surface of the vacuum plenum or its mountingframe. The mounting of the platen transport system 32 to the frame ofthe document handling system 20 allows independent vertical movement ofthe platen transport but prevents its lateral movement and thereformaintains lateral registration of the transport and registration system.It allows the imaging surface of the platen transport and the beltsthereon to closely conform to the plane of the upper surface of theplaten during clamping.

The bottom wall 33a of the vacuum plenum 33, providing the imagingsurface, is formed with sufficient stiffness so as to maintain theflatness of that surface. This may be assisted by stiffening ribs orcorrugations on the interior surface thereof. It may also have a presetbow as described.

The inside surfaces of the lower flights of the belts are supported byand slide over especially designed portions or areas of the backingsurface 33a of the plenum 33. Here it is important to note from FIG. 3that these areas are largely ungrooved, to avoid applying vacuum underthe belts and thereby substantially reduce belt friction with surface33a. The opposite ends of each belt loop are mounted on rollers atopposite ends of the platen transport system 32.

Turning now to the vacuum system for the platen transport system 32, thevacuum source may be provided by a conventional but low pressure fan orblower. Preferably the vacuum source is pneumatically connected to oneside (here the rear) of the manifold 33, as shown in FIG. 2. A very lowlevel of partial vacuum may be applied, e.g. in the order of 20±5 mm(approximately 1 inch) of water static vacuum in the manifold 33 plenum.To operatively communicate this vacuum for document transporting, itmust be provided between the document and the backing or imaging surface33a. With the present system, as shown in FIGS. 3 and 6, this isaccomplished with a large number of small vacuum apertures 53 in themanifold surface 33a. These vacuum apertures 53 here are located inopposite ends of a large number of small vacuum channels 54. Thechannels 54 and their apertures 53 extend in rows across the surface 33aas shown. These concave hemicylindrical channels 54 extend transverselyacross the surface 33a in between adjacent belts 35, across theinterbelt gaps 35a, but do not extend substantially under the belts.I.e., each channel 54 extends between an aperture 53 under one belt edgeonly to another aperture 53 under the adjacent edge of the next adjacentbelt, but not passing under a belt. The pattern of channels 54 extendsacross and widely covers the areas of the belt gaps 35a. The apertures53 are fully covered by the edges of the lower flights of the belts, asshown in FIG. 3. The apertures 53 are not in the interbelt gaps 35a. Allbut the outer edges of the belts 35 ride on smooth, ungrooved,unapertured, areas of the surface 33a. Only the belt edges are over(end) areas of the vacuum channels 54. Thus, only a relatively smallarea of the belts 35 are subjected to any vacuum forces here, andconsequently there is low frictional drag between the belts and their(predominantly smooth) underlying surface 33a. Yet, when a documentsheet is present, the partial vacuum applied to the document frombetween the belts by the channels 54 is more than sufficient to lift thedocument up against the belts, and thereby normally hold both up awayfrom the platen surface, and to maintain sufficient normal force betweenthe document and the belts for non-slip feeding by the belts. Althoughthe channels 54 are relatively shallow, they have sufficientcross-sectional area to conduct the requisite relatively low air flowtherealong with relatively low resistance, and thereby to relativelyuniformly apply the same vacuum level along each channel under the areaof the document between the belts 35. Different vacuum levels might beprovided in different channels 54, but that is not necessary in thecentral area of the surface 33a. However a wider interbelt gap 35a maybe provided there than elsewhere.

Each row of channels 54 is for pneumatically communicating the partialvacuum from its apertures 52 at each end thereof into one gap 35abetween the belts with as little surface 33a perturbation as possible inthe gaps 35a, since these gaps 35a are directly exposed to the copieroptics. The channels 54 have gently sloping side walls as to besubstantially as highly reflective as the rest of the surface 33a andtherefore effectively optically invisible. The depth of the channels 54may be approximately 2 mm, or less. As noted previously, there areprovided additional, deeper, rear side channels 58, also transverse tothe direction of movement of the belts 35, at the rear edge of thesurface 33a. They may be angled to reduce paper edge catching ifdesired.

While the embodiment disclosed herein is preferred, it will beappreciated from this teaching that various alternatives, modifications,variations or improvments therein may be made by those skilled in theart, which are intended to be encompassed by the following claims:

What is claimed is:
 1. In a document handler for presenting documents tothe platen of a copier for copying, comprising a vacuum belt platentransport system for feeding the documents over the platen and into animaging position over the platen, wherein said vacuum belt platentransport system comprises plural document transporting belts movableunder a substantially planar vacuum plenum backing and imagingbackground surface overlying said platen, and vacuum means for applyinga partial vacuum to a document sheet being transported by said movablebelts over said platen, and means for moving said belts, the improvementcomprising:clamping means for moving said vacuum plenum backing andimaging background surface against said platen to flatten said belts anda document thereon against said platen for copying said document, saidclamping means including unclamping means for lifting said vacuum plenumbacking and imaging background surface and said belts slightly away fromsaid platen while supplying said partial vacuum with said vacuum meansto lift a document away from said platen retained on said belts, fortransporting a document with said belts, said unclamping means includingmeans for lifting a first side of said vacuum plenum backing and imagingsurface up away from said platen substantially before the opposite sidethereof, and then subsequently lifting said opposite side, to generate acontrolled air flow for assisting in retaining the document to saidbelts as said vacuum plenum backing and imaging surface is lifted awayfrom said platen, said means for moving said belts being operable whensaid vacuum plenum backing and imaging surface is lifted away from saidplaten and while supplying said partial vacuum with said vacuum means toretain a document against said belts.
 2. The document handler of claim 1wherein said clamping and unclamping means comprises plural cams withdifferent cam rise times connected via cam lifters to lift said firstside of said vacuum plenum backing and imaging surface with a differentmotion than said opposite side by said cams being rotatably driven forclamping and unclamping.
 3. The document handler of claim 1 wherein saidclamping means moves down said first side of said vacuum plenum backingand imaging surface towards said platen beginning slightly before movingdown said opposite side of said vacuum plenum backing and imagingsurface towards said platen, to generate a controlled air flow expulsionof air out from under said vacuum plenum backing and imaging surfaceduring clamping.
 4. The document handler of claim 2 wherein saidclamping means moves down said first side of said vacuum plenum backingand imaging surface towards said platen beginning approximately 5milliseconds before moving down said opposite side, with furtherrotation of said same cams, but beginning said movement of said firstside before said opposite side with different said cam rise timesconfigurations of said cams, to generate a controlled air flow explusionof air out from under said vacuum plenum backing and imaging surfaceduring clamping.
 5. The document handler of claim 2 wherein saidunclamping means, with said rotation of said cams, first lifts saidfirst side of said vacuum plenum backing and imaging surface about 2.5mm away from said platen while said opposite side remains down incontact with the platen, and then lifts said opposite side about 0.8 mm,and then said vacuum plenum backing and imaging surface is leveled bylifting said opposite side from said about 0.8 mm to about 1.75 mm, and,at approximately the same time, said first side is dropped from saidabout 2.5 mm to about 1.75 mm.
 6. The document handler of claim 2wherein clamping and unclamping is accomplished by common rotation ofsaid cams with different cam profiles providing said different cam risetimes, and wherein after said unclamping is at least partially completeda document previously copied is ejected by said platen transport systemand a next document is brought over the platen by said platen transportsystem, while maintaining said vacuum retention of the documents, andthen before the copying of this next document it is clamped against theplaten by moving down both said first side and said opposite side ofsaid vacuum plenum backing and imaging surface with further rotation ofthe same cams but beginning the movement of said first side a fractionof a second before the movement of said opposite side to move saidsurface down at an angle towards said platen which squeegees out airfrom under the document before the final clamping, in which both saidfirst and said opposite sides are flattened against said platen.
 7. Thedocument handler of claim 1 wherein additional vacuum retention meansconnecting with said vacuum means are provided along said first edge ofsaid vacuum plenum backing and imaging surface to provide asubstantially higher partial vacuum holding force to the edge area of adocument overlying said first edge for resisting stripping of thedocument from said vacuum belt platen transport during said unclampinglifting movement.
 8. In a copying method utilizing a document handlerfor presenting documents to the platen of a copier for copying,comprising a vacuum belt platen transport system for feeding thedocuments over the platen and into an imaging position over the platen,wherein said vacuum belt platen transport system comprises pluraldocument transporting belts movable under a substantially planar vacuumplenum backing and imaging background surface overlying said platen, andvacuum means for applying a partial vacuum to a document sheet beingtransported by said movable belts over the platen, and means for movingsaid belts, the improvement comprising the steps of:clamping said vacuumplenum backing and imaging background surface against the platen toflatten said belts and a document thereon against the platen for copyingsaid document by unevenly moving said vacuum plenum backing and imagingbackground surface and said belts down towards said platen, unclampingsaid vacuum plenum backing and imaging background surface and said beltsand a document thereon from said platen by unevenly lifting said surfaceaway from said platen while supplying a partial vacuum with said vacuummeans to lift a document away from said platen retained on said belts,said unclamping including lifting a first side of said vacuum plenumbacking and imaging surface up away from said platen substantiallybefore the opposite side thereof, and then subsequently lifting saidopposite side, to generate a controlled air flow for assisting inretaining the document to said belts as said vacuum plenum backing andimaging surface is lifted away from said platen, and transporting adocument with movement of said belts and with said partial vacuumretaining a document against said belts after said unclamping is atleast partially completed.
 9. The copying method of claim 8 wherein saidclamping moves down said first side of said vacuum plenum backing andimaging surface towards said platen beginning slightly before movingdown said opposite side of said vacuum plenum backing and imagingsurface towards said platen, to generate a controlled air flow expulsionof air out from under said vacuum plenum backing and imaging surfaceduring clamping.
 10. The copying method of claim 8 wherein saidunclamping first lifts said first side of said vacuum plenum backing andimaging surface about 2.5 mm away from said platen while said oppositeside remains down in contact with said platen, and then lifts saidopposite side about 0.8 mm, and then said vacuum plenum backing andimaging surface is leveled by lifting said opposite side from said about0.8 mm to about 1.75 mm, and, at approximately the same time, said firstside is dropped from said about 2.5 mm to about 1.75 mm.
 11. The copyingmethod of claim 8 wherein said clamping and unclamping is accomplishedby rotation of cams with different cam profiles, and wherein after saidunclamping is at least partially completed a document previously copiedis ejected by said platen transport system and a next document isbrought over the platen by said platen transport system, whilemaintaining said vacuum retention of the documents, and then before thecopying of this next document it is clamped against the platen by movingdown both said first side and said opposite side of said vacuum plenumbacking and imaging surface with further rotation of the same cams butbeginning the movement of said first side slightly before said oppositeside to move said surface down at an angle towards said platen whichsqueegees out air from under the document before the final clamping, inwhich both said first and said opposite sides are flattened against saidplaten.